As recombinant DNA technology has developed in recent years, the controlled production by microorganisms of an enormous variety of useful polypeptides has become possible. Many eukaryotic polypeptides, such as for example, human growth hormone, leukocyte interferons, human insulin and human proinsulin have already been produced by microorganisms. The continued application of techniques already in hand is expected in the future to permit production by microorganisms of a variety of other useful polypeptide products. One such useful polypeptide product is human tumor necrosis factor.
Tumor necrosis factor (TNF) is an antitumor substance found in the sera of animals that have been treated with microbial products in two orderly events. The first event is a priming event that causes the activation and proliferation of macrophages and is associated with expansion of reticuloendothelial elements in the liver and spleen. For this priming event, micobacteria such as Bacilus Calmette Guerin (BCG), corynbacteria such as Cornynebacterium parvum and zymosan (yeast cell walls) are effective. The second event is an elicitation event which is necessary for the apperance of TNF in the blood. This requires subsequent treatment of primed animals with lipopolysaccharide (LPS--a major constituent of the cell wall of gram-negative bacteria, also known as endotoxin or bacterial pyrogen). Using these principles, one can obtain sera with similar antitumor and cytotoxic properties from mice, rats and rabbits.
The cellular origin of TNF is macrophages (monocytes), thus, TNF is also referred to as a monokine. TNF causes haemorrhagic necrosis and sometimes complete regression of certain tumors transplanted in mice and shows cytotoxic activity against certain tumor cell lines, but not against normal cells.
Recombinant DNA techniques by which DNA that codes for peptides having TNF activity is introduced into a cell to express TNF or TNF analogs is believed to represent the best hope of inexpensively producing large quantities of TNF. By transforming appropriate host organisms with DNA which encodes the TNF amino acid sequence, genetically modified microorganisms can be employed to product TNF in significant quantities. One barrier to employing recombinant DNA technology for the commercial production of TNF is the need to be able to rapidly and efficiently recover TNF in biologically active form from genetically modified microorganisms which product the desired TNF.